Modern imaging has its roots in the nineteenth century with the advent of film which is used today for diverse applications, including generating common photographs and radiographic medical images using x-rays. During the past ten to twenty years, electronic imaging has become common in many fields and has totally replaced film systems in some applications. The term “electronic imaging” as used herein includes electro-optical imaging in the infrared, visible, and ultraviolet regions of the spectrum, and also in the higher energy regions of the spectrum including soft and hard x-rays and gamma-rays.
In its simplest form, electronic imaging is performed by intercepting radiation in the form of photons from an object of interest or scene to be viewed. The photons may be generated by various sources, such as astronomical sources including the sun and stars, other sources of soft x-rays (photons with energy below 10 kev), x-ray tubes and other sources of hard x-rays (photons with energy equal to or above 10 kev), and gamma ray isotopes or other high energy sources of photons above 50 kev. The photons incident on the object to be viewed can be provided directly from an energy source or can be reflected by one or more objects.
Prior to interception, photons can travel or transit through the earth's atmosphere, the near vacuum of outer space, water, tissue or organs or other elements of a patient in medical applications, other objects to be imaged and examined, or any other medium which may or may not degrade the image or provide information of interest. The photons may pass through lenses, be reflected by mirrors, or be affected by baffles or other components. The intercepted photons may be from one band of the electromagnetic spectrum, from more than one band (i.e., multi-spectral), from many bands (i.e., hyperspectral), or from all bands.
In electronic imaging, the interception of photons is accomplished by imaging, or detector arrays. Detector arrays include a plurality of detector elements, sometimes referred to as pixels, arranged in a linear array or two-dimensional array. The intercepted photons cause analog electrical signals in various forms, such as a voltage, current, or charge, to be generated by the detector elements. Commonly available detector array configurations for electronic imaging include point scan, slit scan, slot scan (sometimes referred to as “push broom”) and fixed two-dimensional image receptors. Such detector arrays are often located in vehicles including aircraft and spacecraft, medical facilities, airports, industrial facilities, homes, offices, and a variety of other locations and can be subsystems of cameras or other equipment.
In many applications, the detector array is enabled to intercept photons for an interval of time (i.e., an imaging interval) and after that interval, the resulting electrical signal generated in each detector element is read out in some fashion and presented to a user or operator of the imager and/or is stored in a memory device for further image processing. It is sometimes necessary or desirable to measure detector output signals many times during a single imaging interval and compute a function of the measured values. For example, in an x-ray detection system described in U.S. Pat. No. 5,665,969 entitled X-RAY DETECTOR AND METHOD FOR MEASURING ENERGY OF INDIVIDUAL X-RAY PHOTONS FOR IMPROVED IMAGING OF SUBJECTS USING REDUCED DOSE, which patent is hereby incorporated herein by reference in its entirety, a weighted sum function of many single photon measurements is computed during each imaging interval.
When a signal couples to more than one imager channel or a signal from one channel couples to another channel, image quality can be adversely affected. Charge sharing is one type of signal coupling in which a single photon impacts more than one detector element, resulting in signal detection in more than one channel. In a photon counting system, charge sharing can cause an extra photon to be counted. Charge sharing can be a more significant problem in systems in which a signal processing function is performed on the detector output signals. For example, in the above-referenced U.S. Pat. No. 5,665,969, the weighting is a function of signal amplitude and, since a detector output signal resulting from charge sharing does not accurately represent the photon energy, weighting can be inaccurately applied.